The present invention is directed to sensoring apparatus which find utility in measuring various aspects of liquid or gaseous mediums. More specifically, the invention provides a means for pressure compensating an amperometric sensor which utilizes a semi-permeable membrane to separate the internal elements and the electrolyte contained therein (and enveloping the elements) from the media being sampled, monitored or analyzed. In this regard reference is hereby made to U.S. Pat. Nos. 3,510,421; 3,577,332; and 3,929,603 which are hereby incorporated by reference and which comprehensively describe the type of measurements or analyses which are commonly made utilizing these means. In addition, these patents also disclose the type membranes and barriers commonly used in the sensors. In addition, U.S. Pat. No. 3,577,332 to Porter et al points out the need for pressure compensating means and procedures and the problems incurred where this is not adequately provided for.
Sensors of the type described and to which the present invention is directed require that the membrane be maintained in a very stable relationship with respect to the surface of the cathode element.
Since the membranes used generally range from less than one to five thousandths inch in thickness, they are obviously quite fragile. Subjecting such a sensor to a pressure differential between the inside and outside will therefore cause movement of the membrane and a resultant change in sensor output.
In order to avoid the above problem and maintain sensor stability, it is necessary to provide a pressure communications path between the electrolyte and the external environment. Such a path may be as simple as a poorly sealed membrane, a drilled passage through the body, or a somewhat more elaborate opening sealed with a flexible diaphraghm. While all of these schemes will provide pressure compensation, they suffer such problems as electrolyte leakage, non-electrical isolation when used in liquid systems, and, in the case of the diaphragm seal, a limited range of pressure compensation.